The use of multiple antennas and receivers can substantially boost the performance of wireless communication systems. For example, antenna diversity and beamforming techniques improve the link budget considerably. Moreover, multiple-input multiple-output (MIMO) systems can raise the channel capacity in the presence of multipath fading. The performance of wireless communication systems could be improved if there existed an efficient way to implement receivers and transmitters using multiple antennas. However, there are several requirements for multiple-antenna systems that have so far made implementation impractical.
One method for implementing a multiple-antenna receiver system is to implement an independent single-path receiver system (i.e., a receiver system that might ordinarily be connected to only a single antenna) for each of the multiple antennas. In this method, each antenna has its own dedicated receiver path for receiving the signal from that antenna. The number of receiver paths is equal to the number of antennas.
However, such an approach greatly increases power consumption and substantially increases the hardware required when compared to a single-antenna receiver system. A single-path receiver system normally consists of a low noise amplifier, a mixer for frequency translation, lowpass or bandpass filter for channel selection, automatic gain control, and an analog to digital converter unit. Assigning a dedicated single-path receiver system to each antenna requires duplication of all the components of the single-path receiver system.
Cost, size, and power constraints frequently render this method impractical. It is desirable to reduce the number of single-path receivers required in a multiple-antenna receiver system, or to otherwise eliminate redundancies among the multiple single-path receivers.
One method for reducing the hardware required for a multiple-antenna receiver is to switch the input connection to a single-path receiver system between multiple antennas in a periodic fashion. For example, if two antennas, Antenna A and Antenna B, were assigned to a single-path receiver system, Antenna A would be connected to the input of the single-path receiver system for a certain time period, then Antenna B would be connected to the input of the single-path receiver system for a similar time period, and so forth.
This switching configuration allows for a single-path receiver to receive the signal from one antenna for some time and the signal from another antenna for another time, thereby reducing the hardware required in the multiple dedicated single-path receiver approach. However, the switching step introduces several problems. For any switching rate, there is always an interfering signal that could corrupt the desired signal as a result of switching. Also, due to latency of the filters required in a receiver, artifacts of one antenna's signal remain in the receive-path for some time after the switch to another antenna has occurred, resulting in interference between the signals from various antennas. Switching between the signals from various antennas results in corruptions and interferences that impair the overall performance of the receiver system.
Similar challenges regarding cost, power, size, and interference exist in implementing multiple-antenna transmitter systems.
What is needed is a system and method for sharing components of a single-path receiver system between multiple antennas without introducing a time-periodic switch.